Vascular endothelial dysfunction has been pointed out as an important index in the early stages of progressive atherosclerosis. The vascular endothelial cell releases many sorts of humoral factors to keep circulatory homeostasis. The vascular endothelial function is inhibited by physical stimuli or various substances including the most important factor, oxidized low-density lipoprotein, which is a kind of modified low-density lipoproteins. For example, the vascular endothelial cell releases nitrogen monoxide as a vasohypotonic factor to adjust vascular tonus. The release of nitrogen monoxide is inhibited by the oxidized low-density lipoprotein.
It has been known that macrophages or vascular endothelial cells internalize the modified low-density lipoprotein through a receptor other than receptors for low-density lipoprotein. The macrophages internalize the modified low-density lipoprotein through scavenger receptors, which have already been structurally analyzed (cf., PCT Patent Japanese Publication Nos. 6(1994)-500765 and 6(1994)-508604, and Japanese Patent Provisional Publication No. 3(1991)-290184). The macrophages are then changed to foam cells, which are specific in arteriosclerotic focus. Since the macrophage scavenger receptors are not found in vascular endothelial cells, it has been anticipated that receptors of another structure are present in the vascular endothelial cells (cf., Hidenori Arai, Toru Kita, Oxidized LDL, Metabolism 28/4, 1991).
For the reasons mentioned above, it is necessary to analyze the structure of a n endothelial receptor for modified low-density lipoprotein, namely t he amino acid sequence of the receptor. However, the structure and the amino acid sequence have not yet been elucidated.